1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor devices and, more particularly, to a method for manufacturing the semiconductor device that has an excellent barrier capability in a miniaturized contact section of the semiconductor device.
2. Description of Related Art
With higher device miniaturization, higher density integration and increased multiple layers of LSI devices, it has become an important subject to develop techniques for embedding wiring material in miniaturized through holes with greater aspect ratios. In the conventional technique, for example, a tungsten plug is embedded in a through hole in a contact section having an aperture diameter of 0.5 xcexcm or smaller and an aspect ratio of 2 or greater. The tungsten plug is required in order to plug the through hole and to prevent reaction between aluminum of the wiring layer and silicon of the silicon substrate. However, such a contact structure tends to result in greater electrical resistance of the tungsten, deterioration of resistance to electromigration and lowered production yield due to its complicated forming process.
Many attempts are being made to develop techniques for embedding aluminum in through holes without requiring a complex embedding process that is currently required for embedding tungsten plugs. However, contact sections that use aluminum require complete countermeasures against junction leak that may be caused by reaction between the aluminum and silicon of the silicon substrate and also require a high barrier capability of a barrier layer.
For example, a barrier layer is formed from a nitride layer of a high melting point metal, such as a titanium nitride layer, that is directly formed by reaction sputtering in a nitrogen atmosphere. Such a barrier layer has the following problems.
{circle around (1)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has an insufficient coverage. Therefore, the formed titanium nitride layer does not provide a sufficient coverage at a bottom portion of a miniaturized through hole that has a high aspect ratio.
{circle around (2)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has large stresses and therefore tends to develop microscopic cracks. As a result, aluminum in the wiring material tends to diffuse and cause junction leaks.
{circle around (3)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has columnar structures. As a result, aluminum tends to diffuse through crystal grain boundaries and cause junction leaks.
{circle around (4)} The crystal orientation of a titanium nitride layer determines a  less than 111 greater than  crystal orientation of an aluminum layer. Because the crystal orientation of a titanium nitride is not always uniform, the plane azimuth in the  less than 111 greater than  crystal orientation of the aluminum layer differs. As a result, the surface of the aluminum layer roughens and mask alignment becomes difficult.
{circle around (5)} Further, a titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, occasionally peels off during film growth because of its own film stresses and therefore tends to generate particles. The particles pollute the surface of the wafer and cause short-circuits, which results in a lowered production yield.
It is an object of the present invention to provide a semiconductor device and a method for manufacturing thereof that enables optimum embedding of a conductive material in miniaturized contact sections having a size of a half-micron or less, and to achieve a high barrier capability without causing junction leaks.
In accordance with one embodiment of the present invention, a semiconductor device is manufactured by the process of forming a through hole in an interlayer dielectric layer that is formed on a semiconductor substrate having a device element. A barrier layer is formed on the interlayer dielectric layer and the through hole. A wiring layer is formed on the barrier layer. The wiring layer may preferably be formed from aluminum or an alloy including aluminum as a main component.
In one aspect of the embodiment of the present invention, the barrier layer is formed by a process including the following steps. (a) A metal layer that forms the barrier layer is deposited on surfaces of the interlayer dielectric layer and the through hole; preferably, the metal layer is formed by a sputtering method or a chemical vapor deposition (CVD) method. (b) Heat treatment is conducted in a nitrogen atmosphere to form a metal nitride layer at least on a surface of the metal layer. (c) The metal nitride layer is brought in contact with oxygen in an atmosphere including oxygen. (d) Heat treatment is conducted in a nitrogen atmosphere to form a metal oxide layer and densify the metal nitride layer.
The step of forming a barrier layer in accordance with an embodiment of the present invention may preferably include step (e) of conducting an oxygen plasma treatment after step (d).
In accordance with a preferred embodiment, a metal layer for a barrier layer is formed first by a sputtering method or a CVD method, and then, the metal layer is subjected to a heat treatment in a nitrogen atmosphere to form a metal nitride layer. As a result, the metal nitride film is formed with a higher cohesiveness with a better coverage at the bottom area of the through hole compared to a metal nitride film that is directly grown by sputtering a metal nitride. Moreover, a barrier layer formed by the process described above has a greatly improved barrier capability, mainly because the metal nitride layer in the barrier layer is densified and the metal oxide layer is formed in the barrier layer.
In accordance with one embodiment, the barrier layer may be formed from a metal oxide layer and a metal nitride layer. In accordance with another embodiment, the barrier layer may be formed from a first metal oxide layer composed of an oxide of a metal that forms the barrier layer, a metal nitride layer composed of a nitride of the metal that forms the barrier layer, and a second metal oxide layer composed of an oxide of the metal that forms the barrier layer.
The metal that forms the barrier layer may preferably include at least one selected from a group consisting of titanium, cobalt, ruthenium, molybdenum, hafnium, niobium, vanadium, tantalum, and tungsten. The metal layer that forms the barrier layer may preferably have a film thickness of about 50-200 nm in consideration of the film thickness of a metal nitride layer and a metal oxide layer that are formed in later steps.
In a preferred embodiment, the heat treatment in step (b) may preferably be conducted at temperatures of about 600-900xc2x0 C. When the heat treatment is conducted in this temperature range, a metal nitride layer is formed with a sufficient film thickness to maintain a higher barrier capability.
In a preferred embodiment, the atmosphere including the oxygen in step (c) may preferably include at least about 10-30% oxygen. This step is employed to bring oxygen in contact with the surfaces of the metal nitride layer.
In a preferred embodiment, the heat treatment in step (d) may preferably be conducted at temperatures of about 600xc2x0 C. or higher. When the heat treatment is conducted in this temperature range, the metal nitride layer is densified better. The nitrogen atmosphere in step (d) may preferably be under normal pressure.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.